Hydraulic equipment

ABSTRACT

A hydraulic apparatus realizes the same function as that of a variable discharge pump by regulating a hydraulic device such as a control valve in a state always operated at a substantially constant number of revolutions with a high efficiency regardless of the type of a hydraulic pump driven by a driving source such as a heat engine or electric motor. This hydraulic apparatus drives a hydraulic pump with a driving source internally or additionally provided with a predetermined amount of inertia, so as to construct a fixed pressure hydraulic source, and further provides peripheral devices corresponding to a required load, so as to open/close a control valve according to a state of a load including an energy accumulating device, a hydraulic motor, or the like such that the load can be supplied with an operating fluid ranging from a low flow rate at a high pressure to a high flow rate at a low pressure.

TECHNICAL FIELD

The present invention relates to a hydraulic apparatus and, moreparticularly, relates to a hydraulic apparatus comprising a hydraulicpump driven by a driving source having a predetermined amount of inertiaor a predetermined amount of moment of inertia, and a load driven by ahydraulic pressure generated by the hydraulic pump.

BACKGROUND ART

In a hydraulic apparatus in which a load such as a hydraulic motor isdriven by a hydraulic pressure generated by a hydraulic pump of fixeddischarge amount type, for example, the amount of operating fluiddischarged from the hydraulic pump is fixed. Therefore, when the amountof operating fluid needed by the load fluctuates, an excess of operatingfluid occurs. Therefore, means for changing the number of revolutions ofthe hydraulic pump and means for adjusting the flow rate by flow rateadjusting means such as a throttle valve or reducing valve have beenemployed in general in order to supply an amount of operating fluidrequired by the load.

However, each of the hydraulic pump and the driving source such as aheat engine or electric motor for driving the hydraulic pump is hard tokeep a high efficiency in all the revolution ranges, whereby theefficiency in the hydraulic apparatus may deteriorate when the hydraulicpump changes its number of revolutions. Also, the flow rate adjustmentconsumes the hydraulic energy as thermal energy, which may lower theefficiency in the hydraulic apparatus.

Hydraulic apparatus using a variable discharge type pump for supplying anecessary amount of operating fluid to the load have also been known.However, such a pump has a complicated structure and is expensive.

Therefore, it is an object of the present invention to provide ahydraulic apparatus which can efficiently supply a load with anoperating fluid within the range from a low flow rate to a high flowrate while keeping a substantially fixed amount of discharge from ahydraulic pump.

DISCLOSURE OF THE INVENTION

For achieving the above-mentioned object, the present invention providesa hydraulic apparatus comprising a driving source inherently oradditionally provided with a predetermined amount of inertia, ahydraulic pump driven by the driving source, a first control valveconnected to a discharge side of the hydraulic pump, a flow path guidinga pass side of the first control valve to an operating fluid tank, and acheck valve having an input side directed to the discharge side of thehydraulic pump; wherein, when the first control valve is switched fromthe pass side to a stop side, an operating fluid whose pressure israised by the inertia is supplied to a load connected to an output sideof the check valve. It will be effective if the switching operation iscarried out repeatedly.

In the hydraulic apparatus in accordance with the present invention, thefirst control valve is switched to the pass side when the hydraulic pumpattains a load torque reaching a value exceeding an output torque of thedriving source and a number of revolutions lowered to a lower limit, andis switched to the stop side after the number of revolutions of thehydraulic pump increases to an upper limit as the load torque of thehydraulic pump decreases. Preferably, the switching operation is carriedout according to a value of detecting means for detecting a state of adriving system or load system connected thereto, or according to a clocktiming from outside.

The hydraulic apparatus in accordance with the present invention maycomprise a first energy accumulating device disposed on the output sideof the check valve, a second control valve disposed in a pipelinebranching off from a pipeline between the first energy accumulatingdevice and the check valve, and a load disposed downstream thereof. Thisload is a hydraulic motor provided with a second energy accumulatingdevice, and is driven by an operating fluid flowing therein from thehydraulic pump and first energy accumulating device when the secondcontrol valve is positioned on the pass side.

In another aspect, the present invention provides a hydraulic apparatuscomprising a driving source inherently or additionally provided with apredetermined amount of inertia, a hydraulic pump driven by the drivingsource, an energy accumulating device and a second control valve bothconnected to a discharge side of the hydraulic pump, and a hydraulicmotor connected downstream thereof; wherein a check valve having aninput side directed to an operating fluid tank is connected between thesecond control valve and hydraulic motor; and wherein the second controlvalve is regulated so as to open/close when an amount of fluid requiredby the hydraulic motor is greater than an amount of fluid discharged bythe hydraulic pump.

When employed in a vehicle, the hydraulic apparatus in accordance withthe present invention comprises a first pump motor for driving a drivingwheel of the vehicle, a third control valve connected so as to guide adischarge side of the first pump motor to an operating fluid tank, acheck valve connected so as to direct an input side thereof to thedischarge side of the first pump motor, a second control valve and afirst energy accumulating device both connected to an output side of thecheck valve, a second pump motor connected to an output side of anothercheck valve having an input side directed to the operating fluid tank ona downstream side of the second control valve, and a second energyaccumulating device driven by the second pump motor; wherein the secondenergy accumulating device is accelerated by an operating fluid suppliedfrom the first pump motor to the second pump motor by a kinetic energyof the vehicle upon switching between pass-side/stop-side positions ofthe second and third control valves.

In another aspect, the present invention provides a hydraulic apparatusapplied to a vehicle, the hydraulic apparatus comprising a first pumpmotor for driving a driving wheel of the vehicle, a third control valveconnected so as to be guided to a check valve and an operating fluidtank both having an input side thereof directed to a discharge side ofthe first pump motor, an energy accumulating device and a fourth controlvalve both connected to an output side of the check valve, a third pumpmotor connected to an output side of another check valve having an inputside directed to the operating fluid tank on a downstream side of thefourth control valve, and a driving source for driving the third pumpmotor; wherein the driving wheel is decelerated by the driving sourceupon switching between pass-side/outside positions of the third andfourth control valves.

The above-mentioned object and other characteristic features andadvantages of the present invention will be clear to those skilled inthe art by reading the following detailed explanations with reference tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a hydraulic circuit diagram showing a hydraulic apparatus inaccordance with the present invention employed as a driving system for avehicle;

FIG. 2 is a schematic explanatory view showing a controller forregulating a control valve shown in FIG. 1, and its related elements;

FIG. 3 is a hydraulic circuit diagram extracting a main circuit of FIG.1;

FIG. 4 is an electric circuit diagram showing an electric circuitsubstantially equivalent to the hydraulic circuit diagram of FIG. 3;

FIG. 5 is a graph showing a P-Q characteristic in the hydraulic circuitconfigured as shown in FIG. 3; and

FIG. 6 is a hydraulic pressure circuit diagram extracting from FIG. 1 aconfiguration for applying the present invention to decelerating avehicle.

BEST MODES FOR CARRYING OUT THE INVENTION

In the following, preferred embodiments of the present invention will beexplained in detail with reference to the drawings.

FIG. 1 is a hydraulic circuit diagram showing a hydraulic apparatus inaccordance with the present invention employed in a driving system for avehicle. In FIG. 1, number 41 refers to a driving source, which ispreferably a heat engine in the vehicle, though other types of drivingsources such as an electric motor may be used. An inertial element,which is specifically a flywheel 45, is attached to a shaft 201 of thedriving source 41. The flywheel 45 is also known as a balance wheel, andaccumulates a rotational energy when driven by the driving source 41 torotate. A shaft 202 is connected to the center of the flywheel 45. Byway of the shaft 201, the driving force from the driving source 41 istransmitted to a hydraulic pump (“third pump motor” in claims) 11 anddrives the latter. When the driving source 41 has a large moment ofinertia, i.e., when the driving source 41 is inherently provided withinertia, the flywheel 45 can be omitted. FIG. 1 shows the whole systemof the hydraulic apparatus, organically combining a plurality of partsin charge of different functions and operations. In this embodiment, ahydraulic pump motor also functioning as a motor is used as thehydraulic pump 11.

By way of pipelines 101, 102, 103, 104, an operating fluid tank 21 isconnected to an inlet port 11 a of the hydraulic pump 11. A filter 22for removing foreign matters from within an operating fluid isinterposed between the pipelines 101 and 102. Disposed between thepipelines 102 and 103 is a check valve 23 having an input side directedto the operating fluid tank 21 and an output side directed to thehydraulic pump 11 via the pipeline 103 (i.e., so as to be able toinhibit the operating fluid from flowing from the pipeline 103 to thepipeline 102).

A pipeline 105 is connected to a discharge port 11 b of the hydraulicpump 11, whereas a pipeline 106 branches off from the pipeline 10S. Apipeline 107 extending to the operating fluid tank 21 is connected tothe pipeline 106 by way of a control valve (“first control valve” inclaims) 1.

A pipeline 108 is connected to the pipeline 105, whereas the pipeline108 is connected to a pipeline 109 by way of a check valve 24. The checkvalve 24 inhibits the operating fluid from flowing from the pipeline 109to the pipeline 108. By way of a pipeline 110, an accumulator (“firstenergy accumulating device” in claims) 31 is connected to the pipeline109.

A pipeline 111 branches off from between the pipelines 109 and 110. Byway of a pipeline 112, a pressure sensor 33 is connected to the pipeline111. The pressure sensor 33 can detect the pressure within the pipelines109, 110 or the pressure accumulated in the accumulator 31. Pipelines113, 114 having a relief valve 32 interposed therebetween are connectedto the pipeline 111. The pipeline 114 communicates with the operatingfluid tank 21. The relief valve 32 opens when the pressure on the outputside of the check valve 24 becomes a predetermined value or higher, inorder to prevent the pressure from exceeding the predetermined value.

A pipeline 115 branches off from between the pipelines 109 and 110, andis connected to a pipeline 116. By way of a control valve (“secondcontrol valve” in claims) 2, a pipeline 119 is connected to the pipeline116. A pipeline 123 extends from the pipeline 119, and is connected toan inlet port 12 a of a hydraulic motor (“second pump motor” in claims)12. The hydraulic motor 12 functions as a load driven in response to theoperating fluid discharged from the hydraulic pump 11. In thisembodiment, a hydraulic pump motor also functioning as a pump is used asthe hydraulic motor 12. A flywheel (“second energy accumulating device”in claims) 42 is attached to the rotary shaft of the hydraulic motor 12.

A pipeline 122 is connected to a junction between the pipelines 119 and123. By way of pipelines 121, 120, the pipeline 122 communicates withthe operating fluid tank 21. A filter 25 is interposed between thepipelines 121 and 120. A check valve 26 for stopping the flow from thepipeline 122 to the pipeline 121 is disposed between the pipelines 121and 122.

A pipeline 124 is connected to an outlet port 12 b of the hydraulicmotor 12. A pipeline 125 branches off from the pipeline 124. By way of acontrol valve 4, a pipeline 126 extending to the operating fluid tank 21is connected to the pipeline 125.

A pipeline 127 extends from the pipeline 124, whereas a pipeline 128 isconnected to the pipeline 127 by way of a check valve 27. The checkvalve 27 inhibits the operating fluid from flowing from the pipeline 128to the pipeline 127. A pipeline 129 extends from the pipeline 128. Byway of a pipeline 130, an accumulator 34 is connected to the pipeline129. The accumulator 34 functions as an energy accumulating device.

A pipeline 131 branches off from between the pipelines 129 and 130. Byway of a pipeline 132, a pressure sensor 36 is connected to the pipeline131. The pressure sensor 36 can detect the pressure within the pipelines128, 130, 131 or the pressure accumulated in the accumulator 34.Pipelines 133, 134 having a relief valve 35 interposed therebetween areconnected to the pipeline 131. The pipeline 134 communicates with theoperating fluid tank 21. The relief valve 35 opens when the pressure onthe output side of the check valve 27 becomes a predetermined value orhigher, in order to prevent the pressure from exceeding thepredetermined value.

A pipeline 135 branches off from the pipeline 129, whereas a pipeline136 is connected to the pipeline 135 by way of a control valve 5. Fromthe pipeline 136, pipelines 138, 142 extend to a control valve 7.

The control valve 7 is also known as a directional control valve, forwhich a 4-port, 3-position spool valve of solenoid type is used in thedepicted embodiment. The pipeline 142 is connected to the P port of thecontrol valve 7, whereas its T port communicates with the operatingfluid tank 21 by way of pipelines 155, 156, 157. A control valve (“thirdcontrol valve” in claims) 8 is interposed between the pipelines 156 and157.

When the control valve 7 is at its center position 7 b, the P and Tports communicate with each other, whereas the A and B ports are closed.When the control valve 7 is at the position 7 a, the P port communicateswith the A port, whereas the T port communicates with the B port. Whenthe control valve 7 is at the position 7 c, the P port communicates withthe B port, whereas the T port communicates with the A port.

One port 13 a of a bidirectional pump motor (“first pump motor” inclaims) 13 is connected to the A port of the control valve 7 by way ofpipelines 143 and 144, whereas the other port 13 b of the pump motor 13is connected to the B port of the control valve 7 by way of pipelines148 and 147. A pipeline 145 is connected to the pipeline 143, whereasone port 14 a of another bidirectional pump motor (“first pump motor” inclaims) 14 is connected to the pipeline 145. A pipeline 146 is connectedto the pipeline 148, whereas the other port 14 b of the pump motor 14 isconnected to the pipeline 146. Driving wheels 43, 44 of the vehicle areconnected to respective rotary shafts of the pump motors 13, 14.

By way of the pipelines 117, 118, control valve 3, and pipeline 137branching off from between the pipelines 115 and 116, an operating fluidcan be supplied between the pipelines 136 and 138 between the controlvalves 5 and 7. A pipeline 159 is connected to the pipeline 117, and isconnected to the pipeline 156 by way of a check valve 30 and a pipeline158. The check valve 30 inhibits the operating fluid from flowing fromthe pipeline 159 to the pipeline 158.

A pipeline 141 is connected between the pipelines 138 and 142 betweenthe control valves 5 and 7. By way of pipelines 140, 139, the pipeline141 communicates with the operating fluid tank 21. A filter 28 isinterposed between the pipelines 140 and 139. A check valve 29 forstopping the flow from the pipeline 141 to the pipeline 140 is disposedbetween the pipelines 140 and 141.

A pipeline 160 branches off from between the pipelines 128 and 129between the hydraulic motor 12 and the control valve 5. By way of thecontrol valve 6, the pipeline 160 is connected to a pipeline 161communicating with the pipelines 103, 104 on the inlet side of thehydraulic pump 12. The pipelines 161 and 159 communicate with each otherby way of pipelines 161, 162 having a control valve (“fourth controlvalve” in claims) 9 interposed therebetween.

The control valves 1 to 6, 8, and 9 are so-called solenoid type on/offvalves, which are regulated together with the control valve 7 toopen/close by a controller 300 constituted by a microcomputer and thelike as shown in FIG. 2. Signals from pressure sensors 33, 36 are fedinto the controller 300. Also fed into the controller 300 are signalsfrom a tachometer 46 for detecting the number of revolutions of theflywheel 42, tachometers 47, 48 for detecting the respective numbers ofrevolutions of the driving wheels 43, 44, and a tachometer 49 fordetecting the number of revolutions of the flywheel 45. The controller300 is configured so as to regulate the opening/closing of the controlvalves 1 to 9 according to these signals.

In thus configured hydraulic apparatus, a case where the energygenerated by driving the hydraulic pump 11 is accumulated into theaccumulator 31 and flywheel 42 respectively acting as the first andsecond energy accumulating devices will now be explained. Reference willalso be made to FIG. 3 extracting a part of the configuration of FIG. 1.

When the driving source 41 is started in the state shown in FIGS. 1 and3, so as to drive the hydraulic pump 11 at a set number of revolutions,the operating fluid is inhaled from the operating fluid tank 21 into thehydraulic pump 11 by way of the pipeline 101, filter 22, pipeline 102,check valve 23, and pipeline 104. The operating fluid taken into thehydraulic pump 11 is discharged therefrom, so as to flow out of thepipeline 105 on the discharge side to the operating fluid tank 21 by wayof the pipeline 106, the control valve 1 set onto the pass side 1 a, andthe pipeline 107. When the control valve 1 is positioned on the passside 1 a, the pipeline 106, control valve 1, and pipeline 107 form anunloaded flow path.

When the position of the control valve 1 is switched from the pass side1 a to the stop side 1 b in this state, the hydraulic pump 11 driven bythe driving source 41 causes the operating fluid to travel the pipelines105, 108 and pass through the check valve 24 toward the load (i.e.,toward the accumulator 31 and hydraulic motor 12). When the position ofthe control valve 1 is switched from the pass side 1 a to the stop side1 b, a pressure higher than a discharge pressure which can becontinuously generated by the hydraulic pump 11 driven at a set numberof revolutions by the driving source 41, i.e., higher than a pressuredischarged from the hydraulic pump 11 during its usual operation, isgenerated. When the control valves 2, 3, 9 are positioned on their stopsides 2 b, 3 b, 9 b, this high-pressure operating fluid is supplied tothe accumulator 31, whereby the energy is accumulated therein.

The reason why the high pressure is generated will now be explained infurther detail. Letting Qm be the torque that can be generated by thedriving source 41 constituted by a heat engine, an electric motor, orthe like, and Qp be the torque of the hydraulic pump 11 driven by thedriving source 41, it is clear that the relationship of Qm=Qp holds whenthe loss is neglected. Assuming that I is the moment of inertia of thedriving source 41 (which substantially equals the moment of inertia ofthe flywheel 45 since the moment of inertia of the driving source 41itself is supposed to be small in the depicted embodiment), and ω be theangular velocity, the inertial torque required for accelerating ordecelerating the driving source 41 can be represented by I·dω/dt. Here,I·dω/dt attains positive and negative values at the time of accelerationand deceleration, respectively.

In this embodiment, the driving source 41 is regulated so as to keep itsset number of revolutions when the control valve 1 is positioned on thepass side 1 a. When the position of the control valve 1 is switched tothe stop side 1 b, the hydraulic pump 11 receives a load, whereby thedriving source 41 is decelerated. Here, as mentioned above, the inertialtorque of the driving source 41 (the inertial torque of the flywheel 45)I·dω/dt is added to Qm, whereby the relationship of Qp=Qm−I·dω/dt holds.Hence, with the inertial torque caused by the deceleration of thedriving source 41 being added, a torque greater than the input torque Qmof the hydraulic pump 11 at the time of usual operation is fed into thehydraulic pump 11. On the other hand, the discharge pressure of thehydraulic pump 11 increases along with the load pressure. As a result,the operating fluid with an increased pressure is supplied to the loadon the downstream side.

Though the foregoing explanation only relates to a case where theoperation of switching the position of the control valve 1 from the passside 1 a to the stop side 1 b is carried out only once, the operation(switching operation) of switching from the stop side 1 b to the passside 1 a and then to the stop side 1 b again may be repeated, wherebythe operating fluid having a high pressure as mentioned above cancontinuously be supplied to the load.

This embodiment can supply a high hydraulic pressure by a smallerdriving source as such, whereby a load can be driven without providing adriving source having an output torque corresponding to the maximum loadtorque needed by the load, which has a great merit in terms of economyas well. The maximum pressure that can be generated can be set by themoment of inertia I of the driving source 41 and the magnitude ofangular acceleration dω/dt.

In the following manner, the switching operation of the control valve 1is carried out. In FIG. 1, the flywheel 45 is provided with thetachometer 49, and the number of revolutions of the driving source 41 isdetected by the tachometer 49. Therefore, it can be recognized from adetection signal from the tachometer 49 if the load torque of thehydraulic pump 11 exceeds the output torque of the driving source 41 andthereby the number of revolutions of the driving source 41 is reduced tothe lower limit. The controller 300 receives the signal from thetachometer 49. If the signal indicates that the number of revolutions ofthe driving source 41 is not higher than the lower limit, the controller300 sends a control signal to the control valve 1, so as to switch itfrom the stop side 1 b to the pass side 1 a, thereby yielding anunloaded state, i.e., a state where the load of the hydraulic pump 11 isremoved. As a result, the load torque exerted on the driving source 41decreases, and its number of revolutions gradually increases to theupper limit or higher. Here, the controller 300 switches the position ofthe control valve 1 to the stop side 1 b again. The timing for thisswitching operation is not limited to the instant when the number ofrevolutions reaches the upper limit, but may be immediately thereafteror immediately therebefore in expectation that the number of revolutionsreaches the upper limit. As such, the control valve 1 repeatedlyexecutes switching operations, thereby continuing its self-excitingaction. The rate of change in the number of revolutions of the hydraulicpump 11, i.e., change in the amount of discharge of the operating fluid,depends on the moment of inertia of the hydraulic pump 11 about itsaxis.

The pressure sensor 33 measures the pressure state on the output side ofthe check valve 24. Therefore, upon recognizing that the value measuredby the pressure sensor 33 reaches a predetermined set value according tothe signal therefrom, the controller 300 switches the position of thecontrol valve 1 from the stop side 1 b to the pass side 1 a, therebyreturning the operating fluid discharged from the hydraulic pump 11 tothe operating fluid tank 21. This operation places the driving source 41into an unloaded state, and increases its number of revolutions.Detecting means used for determining the switching timing as such may benot only the pressure sensor 33 and tachometer 49, but also sensors formonitoring the state of load. When the switching timing is knownbeforehand, etc., the switching can be carried out according to clocktimings from outside without monitoring the state.

When the position of the control valve 2 is switched to the pass side 2a, the operating fluid discharged from the hydraulic pump 11 driven bythe driving source 41 and the operating fluid from the accumulator 31acting as an energy accumulating device flow into the hydraulic motor 12acting as a load, and then return from the pipeline 124 on the dischargeside to the operating fluid tank 21 by way of the pipeline 125, thecontrol valve 4 positioned on the pass side 4 a, and the pipeline 126.This operation drives the hydraulic motor 12, so that the flywheel 42starts rotating and is accelerated. This makes the flywheel 42accumulate energy.

Disposed between the control valve 2 and the hydraulic motor 12 are thepipelines 120, 121, 122 provided with the check valve 26 connected so asto direct its input side to the operating fluid tank 21. The reasontherefor will be explained with reference to FIG. 3. When the number ofrevolutions of the hydraulic motor 12 increases such that the amount offluid needed by the hydraulic motor 12 is greater than the amount offluid discharged by the hydraulic pump 11, the hydraulic motor 12 cannotbe accelerated anymore.

Here, the position of the control valve 2 is switched from the pass side2 a to the stop side 2 b. This operation makes the accumulator 31accumulate the operating fluid, and places the hydraulic motor 12 into afreewheeling state since the operating fluid supplied thereto is notobstructed by the check valve 26. When a predetermined amount ofoperating fluid is accumulated in the accumulator 31, the position ofthe control valve 2 is switched to the pass side 2 a again, whereby theoperating fluid accumulated in the accumulator 31 flows into andaccelerates the hydraulic motor 12. Repeating the switching operation ofthe control valve 2 as such can intermittently accelerate the hydraulicmotor 12 even when the amount of fluid needed thereby is greater thanthe amount of fluid discharged from the hydraulic pump 11. Therefore, alarge amount of flow having a low average pressure for acceleration canbe supplied to the hydraulic motor 12 as a load.

FIG. 4 shows an electric circuit substantially equivalent to thehydraulic circuit of FIG. 3. In FIG. 4, E is a power supply, RL is aload, C1 and C2 are capacitors, Q1 and Q2 are switching devices such astransistors, D1 and D2 are rectifiers, and L1 is an inductor. The powersupply E corresponds to the hydraulic pump 11, whereas the load RLcorresponds to the hydraulic motor 12. The capacitor C1 is the inertia(flywheel 45) of the hydraulic pump 11, whereas the capacitor C2 is theinertia (flywheel 42) of the hydraulic pump 12. The switching devices Q1and Q2 correspond to the control valves 2 and 1, respectively. Therectifiers D1 and D2 correspond to the check valves 26 and 24,respectively. The inductor L1 corresponds to the accumulator 31. Theelectric circuit shown in FIG. 4 is known as a switching power controlcircuit or power regulator circuit, which can adjust the voltage of theload RL by regulating switching frequencies of the switching devices Q1and Q2.

It will be understood that the hydraulic circuit of FIG. 3 substantiallyequivalent to the electric circuit of FIG. 4 operates similarly thereto,and can adjust the number of revolutions of the rotary shaft of thehydraulic motor 12 corresponding to the load RL so as to make it fallwithin a predetermined range by regulating the switching of positions ofthe control valves 1, 2.

FIG. 5 shows an example of results of experiments obtained by using anexperimental apparatus constructed in conformity to the hydrauliccircuit of FIG. 3. In FIG. 5, the solid curve passing the point Pindicates the result of an experiment obtained when the amount ofdischarge was changed while the input was fixed to that in the casewhere the hydraulic pump 11 had a discharge rate of 21.75 liters/min anda discharge pressure of 4.5 MPa. This curve is seen to indicate an idealvariable discharge pump characteristic as compared with thedash-double-dot curve representing theoretical values. Namely, thischart illustrates that the load can efficiently be supplied with theoperating fluid ranging from a low flow rate with a high pressure to ahigh flow rate with a low pressure.

A case where the hydraulic apparatus configured as mentioned above isused for starting and accelerating a vehicle will now be explained. Thestarting is just a case where the initial speed to be accelerated iszero, and thus will be explained simply as acceleration in thefollowing. The acceleration of the vehicle includes three methods, i.e.,one using the driving source 41 alone, one using only the flywheel 42operating at a preset number of revolutions, and one using both thedriving source 41 and the flywheel 42.

When accelerating the vehicle with the driving source 41 alone, thecontrol valves 2, 5, 6, 9 are set to their close positions or on thestop sides 2 b, 5 b, 6 b, 9 b, whereas the control valve 8 is set to itsopen position or on the pass side Ba. On the other hand, the controlvalve 7 is switched from the center position 7 b to the position 7 a.

Thereafter, the operating fluid discharged from the hydraulic pump 11driven by the driving source 41 is supplied to the pump motors 13, 14,so as to accelerate rotations of the rotary shafts of the pump motors13, 14, and rotations of the driving wheels 43, 44. There are also threemethods in this case. The first method fixes the position of the controlvalve 3 to the pass side 3 a, and repeatedly switches the control valve1 between the pass side 1 a and stop side 1 b according tocircumstances. The second method fixes the control valve 1 to the stopside 1 b, and repeatedly switches the control valve 3 between the passside 3 a and stop side 3 b according to circumstances. The third methodswitches between positions of both the control valves 1, 3 as required.The control valve 5 may switch its positions according to circumstances.Acceleration can also be achieved when an undepicted control valve isdisposed in the pipeline 138 and operated in a manner similar to thatmentioned above.

Here, note that the control valve 3 corresponds to the control valve 2,the check valve 29 to the check valve 26, the control valve 8 to thecontrol valve 4, and the pump motors 13, 14 to the hydraulic motor 12.The driving wheels 43, 44 also function as inertial elements which canbe driven by the inertia of the vehicle. Since the switching operationsof the control valves 1, 3, 8 are equivalent to those of the controlvalves 1, 2, 4 mentioned above, their overlapping explanations will beomitted.

When accelerated by the flywheel 42 alone, it is necessary for theflywheel 42 to operate at a number of revolutions falling within apreset range. The flywheel 42 operating within the preset range becomesthe driving side. Therefore, the control operation for accelerating thedriving wheels 43, 44 of the vehicle on the driven side is carried outin a state where at least the control valves 3, 6, 9 are positioned ontheir stop sides 3 b, 6 b, 9 b. Then, the positions of the controlvalves 4, 5, 8 are switched, so as to supply the pump motors 13, 14 withthe operating fluid. There are also three methods in this case. In thefirst method, while the control valve 8 is positioned on the pass side 8a, the control valve 5 is fixed to the position on the pass side 5 a,and the position of the control valve 4 is repeatedly switched betweenpass side 4 a and the stop side 4 b according to circumstances. Thesecond method fixes the control valve 4 to the position on the stop side4 b, and repeatedly switches between positions of the control valve 5.The third method repeatedly switches between positions of both thecontrol valves 4, 5.

Here, note that the hydraulic motor 12, control valve 4, check valve 27,accumulator 34, control valve 5, check valve 29, pump motors 13, 14, andcontrol valve 8 correspond to the hydraulic motor 11, control valve 1,check valve 24, accumulator 31, control valve 2, check valve 26,hydraulic motor 12, and control valve 4, respectively.

The vehicle can also be accelerated by both the driving source 41 andflywheel 42 if the control valves are repeatedly switched according tocircumstances as mentioned above.

The switching operation according to circumstances will now beexplained. The amount of operating fluid varies depending on the speedof the vehicle, but can be determined by detecting states such asnumbers of revolutions of the pump motors 13, 14 on the driven side.Similarly, the amount of fluid that can be supplied can be determined bydetecting the number of revolutions of the pump motor 13 or 14 on thedriving side and the like. Means for detecting the state of rotation arethe tachometer 46 attached to the flywheel 42, the tachometers 47, 48attached to the pump motors 13, 14, and the tachometer 49 attached tothe flywheel 45. Means for detecting the state of the operating fluidare the pressure sensors 33, 36. In response to signals from thesesensors, the controller 300 causes the control valves to carry outswitching operations. Flow rates can also be measured by flow ratesensors and the like.

For example, the controller 300 switches the position of the controlvalve 4 to the pass side 4 a upon recognizing that the sensor 36 reachesa preset upper pressure, and switches the position of the control valve4 to the stop side 4 b again when the sensor 36 reaches a preset lowerpressure, thus carrying out acceleration by repeating this switchingoperation. Changing the upper and lower pressure limits as such canregulate the degree of acceleration. In the case where the states on thedriving side and driven side are grasped beforehand, control valves canbe switched by control signals and clocks outputted from the controller300 as well.

Though the operating fluid for accelerating the vehicle includes thepart passing the control valve 3 from the hydraulic pump 11 and the partfrom the hydraulic motor 12, the part accumulated in the accumulator 34can also be used. Namely, while in a state where the flywheel 42attached to the hydraulic motor 12 is rotating, the hydraulic motor 12can operate as a hydraulic pump, so as to cause the accumulator 34 toaccumulate the operating fluid from the operating fluid tank 21, andthus accumulated hydraulic fluid can be used for accelerating rotationsof the rotary shafts of the pump motors 13, 14. The operating fluidpassed through the pump motors 13, 14 is returned to the operating fluidtank 21 by way of the control valve 8.

A case where the vehicle is decelerated while in an advancing state willnow be explained. The deceleration includes two patterns, i.e., adecelerating operation accompanying regeneration and a deceleratingoperation without regeneration. First, the decelerating operation withregeneration will be explained. When the vehicle advances, the ports 13b, 14 b of the pump motors 13, 14 become the discharge side. Thepipeline 158 on the input side of the check valve 30 is connected to thepipeline 155 connected to the ports 13 b, 14 b by way of the controlvalve 7 at the position 7 a, whereas the output side of the check valve30 is connected to the input side of the control valve 2. In thisconfiguration, in a state where the pump motors 13, 14 continue theirrevolutions because of the inertia of the vehicle, the pump motors 13,14 become the driving side, whereas the driven side is the hydraulicmotor 12 to which the flywheel 42 is connected. When accelerated, theflywheel 42 becomes a load, thereby decelerating the vehicle. Thecontrol operation can be explained as in the case of accelerating thevehicle with the flywheel 42, in which actions similar thereto arecarried out while the control valves 5 and 4 to switch their positionsact as the control valves (second and third control valves) 2 and 8,respectively.

The decelerating operation without regeneration will now be explained.From FIG. 1, FIG. 6 extracts a circuit configuration required fordeceleration without regenerating a kinetic energy of the vehicle.Actions in this configuration will now be explained. When the vehicle isdecelerated, the operating fluid discharged from the pump motors 13, 14flows into the hydraulic pump 11 acting as a motor. The hydraulic pump11 is linked to the driving source 41 and thus acts as a so-calledengine brake, thereby decelerating the vehicle. The control operationcan be explained as in the case of accelerating the vehicle with theflywheel 42, in which actions similar thereto are carried out while thecontrol valves 5 and 4 to switch their positions act as the controlvalves 9 and 8, respectively.

The regenerating action at the time of decelerating the vehicle can becarried out by energy accumulating devices such as accumulators andflywheels mentioned above. Even when regeneration is not necessary inparticular, the operating fluid discharged from the pump motors 13, 14flows into the hydraulic pump 11, so that the driving source 41 havingthe hydraulic pump 11 linked thereto becomes a load and consumes energy,whereby deceleration can be achieved without consuming the energy asthermal energy by relief valves and the like. This can prevent theoperating fluid from raising its temperature and deteriorating.

For moving the vehicle in reverse, it will be sufficient if the positionof the control valve 7 is switched to the position 7 b.

For coasting the vehicle, if the position of the control valve 8 isswitched to the pass side 8 a while at least the control valves 3, 5, 6are positioned on their stop sides 3 b, 5 b, 6 b, the pipelines 139,140, 141 connected between the pipelines 138, 142 construct afreewheeling circuit of the pump motors 13, 14, whereby the operatingfluid returns to the operating fluid tank 21 by way of the controlvalves 7, 8. Under this condition, the vehicle attains a coasting state.As the control valve 7, one different from the type shown in FIG. 1 maybe used, so as to construct pipeline parts for the pump motors 13, 14 asa closed circuit, thereby achieving a coasting state.

When the flywheel 42 is operating at a preset number of revolutions, thecontrol valve 6 can be opened and closed, so as to supply the hydraulicpump 11 with the operating fluid from the hydraulic motor 12, therebystarting the driving source 41, etc.

In the present invention, the pump motors 11 to 14 can be pumps withfixed discharge amounts. This enables reversible actions which cannot berealized by pumps with variable discharge amounts, thereby making itpossible to utilize engine braking effects of motors on the drivingside.

Though preferred embodiments of the present invention are explained indetail in the foregoing, the present invention is not limited to theabove-mentioned embodiments, and elements satisfying functions requiredin the present invention can be used as a replacement. The systememploying the hydraulic apparatus in accordance with the presentinvention is not limited to the vehicle.

INDUSTRIAL APPLICABILITY

By switching the control valves according to the load required, thepresent invention can efficiently supply the load with the operatingfluid discharged from a fixed pressure hydraulic source ranging from alow flow rate at a high pressure to a high flow rate at a low pressure,whereby a heat engine, an electric motor, or the like acting as adriving source can be used in the vicinity of its most efficient numberof revolutions. Also, the driven hydraulic pump can always be operatedat a highly efficient number of revolutions regardless of types such aswhether it is a fixed or variable discharge pump. Therefore,conventional devices can efficiently be operated, whereby the system asa whole can attain a higher efficiency.

Also, in this operation, the energy discarded as an excess inconventional fixed discharge pumps will not be lost, so that theoperating fluid can be prevented from raising its temperature anddeteriorating, whereby actions as a variable discharge pump can berealized without changing the capacity by a pump. Therefore, a fixeddischarge pump can realize the same function as that of a variabledischarge pump without using any expensive variable discharge pump.

When used as a driving apparatus for a vehicle or the like, thehydraulic apparatus of the present invention can collect a kineticenergy of the traveling vehicle or the like, so as to realizeregenerative braking, or cause the motor acting as a driving source tofunction as an engine brake, thus allowing pump motors to effectreversible actions, whereby operations with a high efficiency arepossible. When there is no regeneration, the operating fluid can beprevented from raising its temperature.

1. A hydraulic apparatus comprising: an operating fluid tank; a drivingsource inherently or additionally provided with a predetermined amountof inertia; a hydraulic pump driven by the driving source, said pumpadapted to suck in the operating fluid from said tank; a first pipelineextending the discharge port of said hydraulic pump toward a load; asecond pipeline branching off from said first pipeline and extending tosaid tank; a first open/close valve interposed in said second pipeline;and a check valve interposed in said first pipeline on a downstream sideof a branching point between said first and second pipelines, said checkvalve adapted to flow the fluid in only one direction from saidhydraulic pump toward said load, wherein pressure of the fluid is raisedby said inertia and the fluid is supplied to said load when the positionof said first open/close valve is repeatedly switched between a passside and a stop side thereof.
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 4. A hydraulicapparatus according to claim 1, wherein an operation of switching theposition of said first open/close valve between the stop side and thepass side is carried out according to a value of detecting means fordetecting a state of a driving system or load system connected to saidhydraulic apparatus.
 5. A hydraulic apparatus according to claim 1,wherein an operation of switching the position of said first open/closevalve between the stop side and the pass side is carried out accordingto a clock timing from outside.
 6. A hydraulic apparatus according toclaim 1, wherein the position of said first open/close valve is switchedto the pass side when said hydraulic pump attains a load torque reachinga value exceeding an output torque of said driving source and a numberof revolutions lowered to a lower limit; and wherein the position ofsaid first open/close valve is switched to the stop side after thenumber of revolutions of said hydraulic pump increases to an upper limitas the load torque of said hydraulic pump decreases.
 7. A hydraulicapparatus according to claim 6, wherein an operation of switching theposition of said first open/close valve between the stop side and thepass side is carried out according to a value of detecting means fordetecting a state of a driving system or load system connected to saidhydraulic apparatus.
 8. A hydraulic apparatus according to claim 6,wherein an operation of switching the position of said first open/closevalve between the stop side and the pass side is carried out accordingto a clock timing from outside.
 9. A hydraulic apparatus according toone of claims 1, 4, 5, 6, 7 and 8, wherein said hydraulic pump is a pumpwith a fixed discharge amount.
 10. A hydraulic apparatus according toone of claims 1, 4, 5, 6, 7 and 8, comprising: a first energyaccumulating device interposed in said first pipeline on the output sideof said check valve; and a second open/close valve interposed in saidfirst pipeline downstream of said first energy accumulating device;wherein said load is driven by the fluid flowing therein from saidhydraulic pump and said first energy accumulating device when saidsecond open/close valve is positioned on a pass side thereof.
 11. Ahydraulic apparatus according to claim 10, wherein said load is ahydraulic motor provided with a second energy accumulating device.
 12. Ahydraulic apparatus according to claim 11, wherein the second energyaccumulating device is a flywheel attached to the hydraulic motor.
 13. Ahydraulic apparatus comprising: an operating fluid tank; a drivingsource inherently or additionally provided with a predetermined amountof inertia; a hydraulic pump driven by the driving source, said pumpadapted to suck in the operating fluid from said tank; a hydraulicmotor; a first pipeline extending the discharge port of said hydraulicpump toward said hydraulic motor; an energy accumulating deviceconnected to said first pipeline; an open/close valve interposed in saidfirst pipeline downstream of said energy accumulating device; a secondpipeline branching off from said first pipeline between said hydraulicmotor and said open/close valve and extending to said tank; and a checkvalve interposed in said second pipeline, said check valve adapted toflow the fluid in only one direction from said tank toward saidhydraulic motor, wherein the switching operation of said open/closevalve that the position of said open/close valve is switched to a stopside when an amount of fluid required by the hydraulic motor is greaterthan an amount of fluid discharged by the hydraulic pump and that theposition of said open/close valve is switched to a pass side when thefluid is accumulated in said energy accumulating device is repeated. 14.A hydraulic apparatus for use in a driving system of a vehicle, saidapparatus comprising: an operating fluid tank (21); a first pump motor(13 or 14) for driving a driving wheel (43 or 44); a first pipeline(155, 156, 157) for leading the operating fluid discharged from saidfirst pump motor toward said tank; a first open/close valve (8)interposed in said first pipeline; a second pump motor (12); a secondpipeline (158, 159, 117, 116, 119, 123) branching off from said firstpipeline between said first pump motor and said first open/close valveand extending to an inlet port of said second pump motor; a first checkvalve (30) interposed in said second pipeline, said first check valveadapted to flow the fluid in only one direction from said first pumpmotor toward said second pump motor; a first energy accumulating device(31) connected to said second pipeline between said first check valveand said second pump motor; a second open/close valve (2) interposed insaid second pipeline between said first energy accumulating device andsaid second pump motor; a second energy accumulating device (42) adaptedto be driven by said second pump motor; a third pipeline (122, 121, 120)branching off from said second pipeline between said second pump motorand said second open/close valve and extending to said tank; and asecond check valve (26) interposed in said third pipeline, said secondcheck valve adapted to flow the fluid in only one direction from saidtank toward said second pump motor, wherein the fluid discharged fromsaid first pump motor by a kinetic energy of said driving wheel issupplied to said second pump motor to accumulate energy in said secondenergy accumulating device upon repeatedly switching between a pass sideposition and a stop side position of said first open/close valve and/orsaid second open/close valve.
 15. A hydraulic apparatus for use in adriving system of a vehicle, said apparatus comprising: an operatingfluid tank (21); a first pump motor (13 or 14) for driving a drivingwheel (43 or 44); a first pipeline (155, 156, 157) for leading theoperating fluid discharged from said first pump motor toward said tank;a first open/close valve (8) interposed in said first pipeline; a secondpump motor (11); a second pipeline (158, 161, 162, 104) branching offfrom said first pipeline between said first pump motor and said firstopen/close valve and extending to an inlet port of said second pumpmotor; a check valve (30) interposed in said second pipeline, said checkvalve adapted to flow the fluid in only one direction from said firstpump motor toward said second pump motor; an energy accumulating device(31) connected to said second pipeline between said check valve and saidsecond pump motor; a second open/close valve (9) interposed in saidsecond pipeline between said energy accumulating device and said secondpump motor; and a driving source (41) for driving said second pumpmotor, wherein said driving wheel is decelerated as a load uponrepeatedly switching between a pass side position and a stop sideposition of said first open/close valve and/or said second open/closevalve.